When tunnels are constructed, in order to prevent scattering of crushed stones and dust, iron plates or used mats are set up at a certain distance from working faces, or nylon woven fabric is suspended like a curtain.
However, when iron plates or used mats are set up, their handling is troublesome because they are heavy. When a nylon woven fabric is suspended, although the woven fabric is lightweight and is readily handled, it is destroyed by several times of blasting operations because of its low strength and becomes unusable.
As a sheet to be used for this purpose, Japanese Patent Kokai No. 62-284900 discloses an explosion-proof sheet for excavation tunnels which comprises an external air bag and an internal sheet of high tenacity fibers such as aramid fibers. Japanese Patent Kokai No. 63-80198 discloses a material having high-impact properties such as that used for helmets, bulletproof jackets and the like which comprises a fabric of polyolefin multifilaments having high strength and high modulus.